Method of diamond drilling



5 21 9 12 1 I mm: non GROSS REFEREM y 1945- J. KURTZ EIAL 2,

METHOD OF DIAMOND DRILLIHG Filed June 26, 1943 2 Sheets-Sheet l ATTOKEVIEY eierrted May 29, 1945 i were METHG-B OF DIAMQND DRILLING Delaware Application June 26, 1843, Serial No. 92,365

4 Claims.

invention relates to a method of percrating diificultiy workable materials such as discorundum and similar herd substances. More particularly it relates to a method of drilling diamond dies.

In the manufacture of diamond dies, it has geriorally been the practice to drill a conical cavity more than half through the diamond and then drill another cavity from the opposite side until a break through occurs, thus completing the perforation. Ordinarily a diamond splint is used to start a smell conical hole which is subsequently enlarged by using a. revolving steel needle coated with diamond dust and oil. When this cavity is completed to more than half way throes the diamond, a similar operation is carried out from thopposite side uhti the two cavities meet. The axes of the two cavities must with the methods and apparatus generall in use in work or this kind, it is ext emely difficul: to effect exactly symmetrical conical cavities and to ensure that the axes of the cavities drilled from opposite sides will coincide. A high degree of eccuracyin this respect is necessary and even very slight deviation from axial symmetry will greatly impair the usefulness and eficiency of the die.

Moreover, by method of drilling, particu- Early when dril fine sized holes, very little bearing surface in the passage through the die is obtainable excep: with great difficulty. This is for the reason when the break through is made, the edge at the point or breaking through, where the two cavities meet, is ordinarily quite sharp and may no: he truly circular in contour with the cone s "ces fiaring away on each side. It is hi 1e, however, that at the point of tires the passage should be for a short distance cylindrical, in order to provide bearing surfaces to ensure exact diameters in the wire which is to be drawn therethrough.

It has been proposed to drill diamonds and other hard materzals by means of an electric spark r currents of low voltage. as. for instance. 116 volts. or even as low as 40 to 50 volts, and at low frequencies such as 50 cycles or even by direct current. But while this method works moderately well in drilling glass or quartz, it has or been appreciy successful in drilling diamonds or COILlQdUZXr. In addition to this objection, the method provides no setter bearing surfaces than the old method of drilling with dis.- mend dust.

It is an object of the present invention to provide a method of drilling dliiicultly workable ma.-

terials such as diamonds or corundum by an electricei method and to produce thereby perfectly symmetrical perforations.

It is a. further object to arise a. drilling which is not only symmetrical but. w. ich possesses an adequate bearing surface within the perforation.

It is a further object to provide a controllable process of rapid drilling with a substantial saving of labor and material.

According to the present invention, the diamood or corundurn is first prepared to be drilled by makfig two exactly perallelfeces. This can be done in known manner by first mounting the diamond in iced or silver solder in a suitable holder and lapping the surfaces fiat by means of an iron disk impregnated with diamond powder. in order that the contour or the hole later to be driile may be readily examined, two additional parallel faces are lapped and polished at right angles to the first two faces.

The diamond is next centered on one side and the entrance started in any one of a number of ways known in the art; for instance, the position where the entrance is to be made must first be carefully determined. Thereupou, a diamond splint held in a suitable holder is pressed against the center point on the face of the rotating diamond, thus cutting a small conical hole in the diamond.

When the diamond has been thus spotted, a tungsten needle having suitable electrical connections is brought to bear on the small starting hole thus bored. The diamond is placed in an electrolyte he a, container in which also an electrode is introduced spaced some distance from the diamond. A high frequency electric current, the power output or which may be varied so as to give approximately 100 watts at a. voltage of from 350 to 1500 volts at a frequency of about 25 kilocycles or over, is passed through the needle and a conical cavity is rapidly drilled to a distance somewhat more than half way through the diamond.

A hole is then drilled in like manner from the opposite side. It is spotted with a diamond splint as in the first instance great care must be exercised and the exact axis of the first conical hole must be determined with the aid of microscopic cross hairs in order to ensure symmetry of the boring and exact coincidence of the axes of the two cavities. The dri .;g on this side is not carried to the point of break through. The contour of the two cavities, w' ile preferably conical, may be controlled by shaping the tungsten needle to the contour desired.

The diamond is now removed from the electrolyte and dried and two tungsten needles in suitable electrical connections are brought to hear from opposite sides of the diamond in the conical cavities formed as described. The drilling then proceeds withoutan electrolyte in a high frequency circuit. The high frequency energy may be generated by means of two adjustable high decrement quench snarl: gaps, a primary high frequency esclter circuit being tuned and coupled to a high voltage tank circuit. It will be apparent, however, that similar high frequency currents may be produced circuits including vacuum tubes instead of spark gaps,

The high frequency current passes from needle point to needle point through the diamond and the two conical cavities-are rapidly joined by a cyllnairical passage. This cylindrical passage. when polished in the usual marine constitutes a bearing su face insuring exact diameters to wires drawn thercthrough.

The invention will be more clearly uncierstoorl from the drawings. in which Fig. 1 represents the diamond spotted and centered in the known man ner; Fig. 2 is a diagrammatic representation of the apparatus in circuit for holding the tungsten "needle; 3 represents the diamond with conicsi borlngs on both sides efiected in this apps. ratus; Fig, 4 represents diagrammatically the dry drilling apparatu employing two tungsten needles; Fig. 5 represents an operative circuit for use in the aproratus of Fig. 4; and Fig. 6 illustrates the diamond as finally bored.

The diamond after being first provided with polished lapped parallel sides, as hereinbefore dcscribed, is then spotted, this being done in any known manner as, for instance, by grinding with a steel needle or a diamond splint to provide the slight depression a on the upper side. "the diamond is then ready for drilling which is done in the apparatus illustrated in Fig. 2. The spotted diamond i is paced upon a glass block 2. The glass block is placed in the glass cup 3 and an electrolyte such as nitric or sulphuric in quantity just sufficient to cover the diamond i is introduced into the glass cup 3. An electrode 5 is also placecl in the glass cup 3 and in the electrolyte Q, spaced some distance from the diamond l. The shaft *3 holds the needle i which is centered thereon and the shaft is then rotated by the pulley 8 connected to a suitable source of power, not shown. The shaft 8 is slidably mounted in the arms 5% and ill or the standard ii and it is new brought down into the previously centered hole a of the diamond l. The variable high frequency generator l2, when the switches M and it are closed, delivers a high frequency current at a frequency of 50 iiilocycles or more through the lead is to the shaft 8, through the shaft to the needle I, through thediamonrl i, electrolyte electrode 5 and return line 55. When the circult is thus closed, an arc will be observed to pass between the needle point 1 and the diamond i and the nature of this are can be controlled by controlling the shape of the needle and the strength and height of the electrolyte.

The strength of the arc is, of course, controlled and determined by the high power output of the high frequency generator l2, and it is generally the case that at the beginning a. higher voltage is employed than in the later stages, when the drilling proceeds rapidly with the high frequency generator i2 delivering about 100 watt: power at 2: frequency of 2D mcgacycles.

Control of the desired contour of the hole drilled may be effected by shaping the needles, it being possible to obtain exceedingly fine holes with the exceedingly sharp points on the needle. It is, however, frequently the case that alter the discharge has. continued for ashort period, say five to ten minutes, the caiity bored hrs become somewhat enlarged anal also the shape of the needle has changed. A new sharp needle may then be inserted as desires, the circuit closed again and the action proceeds as before outlined. In some cases it is desirable to change the needle from time to time in order to control the s ze and contour of the drilling by supplying new needles of the proper size and con wur to effect the desired end, it being understood that in the fine! drilling very sl'nrp slender needle points may be employed to obtain very fine perforations.

At this stage of the curl n' g the dicmono is removed and the reverse side is then operated upon mono while the cavity is on the under side is seento be less than half way through the diamond.

The diamond is then removed from the elec- 'trolyte, dried and placed in the apparatus illustrated diagrammatically 121 Fig. l. In thi apps.- ratus the high frequency sperh coil 2% is connected to the shaft 22 which holds the tungsten needle 23. The high frequency spark coil 24 is connected to the shaft 25 which hold the tungsten needle 25. The diamond 27 is placed on the glass block 28 carried by the arm 29 of the standard El The needle 23 bears on the conical cavty a on the upper side of the diamond 2? and the needle 28 passes through the glass block 28 and bears on the conical cavity 27 in the bottom of the diamond 2?. The glass block 28 acts as insulation for the tungsten needle 25.

The circuit will be understood from Figs. 4 and 5. A source or alternating current 31 delivers a current of about volts at 60 cycles when the switch 32 is closed. The step up transformer 33 raises this to 10,009 to sense volts and serves the spark gap coil 2! through leads 35 and 35. The spark gap coil 2! of Fig. 4 includes the spark gap 35. the condensers 3! and 38, and the coil 39 shown in Pig. 5. Similarly, the step up transformer ll delivers a current of 10,006 to 30,000 volts to the spark gap coil 24 through the leads 5! and 2. The spark gap coil 26 of Fig. 4 includes the spark gap 43, condensers 4 and 5, and the coil es shown in Pig. 5.

When the switch 32 is closed, a high frequency current flows from the transformers 33 and 40 through the needles 23 and 2E and through the shortest distance through the diamond which is the axis of the conical cavities a and b and e cylindrical perforation between he two cavities is rapidly effected. The diamond is thus finished in the form represented by 6 in which the upper conical cavity a and the lower conical cavity 6 are united by the cylindrical passage 0.

By the method of this invention, irillings as small as one quarter'oi one thousandth (.00025) of an inch may be easily and rapidly bored, and it is possible to preserve the greatest accuracy in securing axial symmetry between the borings on the top and bottom of the diamond.

Having thus described our invention, what we claim is:

1. The method of manufacturing a die of dis.-

mend or like materiel comprising the slep of drilling, on opposite sides of said diamond, conical cavities having coinciding axes by subjecting said diamond to the actioo of high frequency electrical current passing between 9. needle point and anoiher electrode in an electrolyte, and then join m said conical cavities by drilling a, cylindrical axial passage by the action of high frequency electrical current passing between opposed needle points extending into said conical cavities in the absence of an electrolyte.

2. The method of drilling diamonds or similar difzculily workable materiels which comprises & first step of immersing the diamond in an electrolyte, brim a tungsten needle to bear on a prel'iousiy formed small cavity in the-diamond, p wns a. high freq en y currentbetween said needle and an electroele which extends into said electrolyte until a conical cavity is drilled more than half way ill-cough said diamond; then z-eversing said dlaznomi and drilling a conical cavit with coinciding axis in similar manner from the opposite slrle to a, distance short of break through; end linen. in a second step, placing said diamond between two tungsten needles without an electrolyte, said needles ba ing on the two conical cavities and passing a high frequency current at. e voltage of about 1%,933 volts to 30,000

volts bczween solo needles, thereby drilling :3 cylindrical passage connecting said two conical cavities.

3. The method of manufacturing a die of diamono or like mcteri 21 comprising the step of uniting the amxes of opposed coaxial conical cavities previously formed in said diamond by a cylindrical coaxial passage formed by centering needles in each of said cones and a high frequency electrleal current between the points of said :lcedles in the absence of an electrolyte.

4. The method of drilling cavlles in a diamond or like material which cempriss freely supporting said material to be drilled on an insulating block in an electrolyte, centering a tungsten needl on said diamond and passing a. high fre quency current between said nee-file and another electrode spaced from said diamond in said electrolyte.

JET/OB KURTZ. JAMES B. WALDIE. JOSEPH SPINA. 

